Global fisheries and conservation - PowerPoint PPT Presentation

Global fisheries and conservation. Before moving on from fishes to the tetrapods, I want to devote some time to fishing. It is a sad fact that global fish stocks have been enormously depleted and in most places fish populations are a pale shadow of their former abundance.

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For example: Captain John Smith describing tributaries of the Chesapeake in 1608 “… in diverse places that abundance of fish lying so thicke with their heads above the water, as for want of nets we attempted to catch them with a frying pan, but we found it a bad instrument to catch fish with. Neither better fish more plenty or variety had any of us ever seene, in any place swimming in the water than in the Bay of the Chesapeack, but there not to be caught with frying pans.”

Captain John Smith again: Having grounded on an oyster bed in the Potomac as the tide was going out “…we spied many fishes lurking amongst the weeds on the sands, our captaine sporting himself to catch them by nailing them to the ground with his sword, set us all a fishing in that manner, by this devise, we tooke more in an houre than we all could eat.”

John Cabot voyaged to Newfoundland in 1497. The Milanese ambassador to London reported what he had heard from Cabot about the fishing there: “they assert that the sea there is swarming with fish, which can be taken not only with the net, but in baskets let down with a stone, so that it sinks in the water. I have heard this Messer Cabot state so much.”

Two centuries later Pierre de Charlevoix in 1719 described the Grand Banks of Newfoundland “What is called the great bank of Newfoundland … you find on it a prodigious quantity of shell-fish, with several other sorts of fishes of all sizes, most part of which serve for the common nourishment of the cod, the number of which seems to equal that of the grains of sand which cover this bank. For more than two centuries since, there have been loaded with them two to three hundred ships annually, notwithstanding the diminution is not perceivable.”

In 1992 the Canadian Government placed a two year moratorium on cod fishing, which was extended indefinitely and remains in place today. In 2003 the two main populations of Atlantic cod were added to Canada’s endangered species list.

Up until the early 20th century, cod-fishing had been almost exclusively by schooners using hand lines but then steam trawlers were introduced to North America. With their greater fishing power the steam trawlers soon replaced the schooners and had become common by the 1920’s.

Around the same time fast-freezing technology was developed and the frozen fillet entered the marketplace.

In 1930 an estimated 37 million haddock were landed in Boston. However, even more were discarded because small mesh nets caught fish indiscriminately and more than two juvenile haddock were discarded for each adult landed.

Not surprisingly, haddock numbers crashed falling to 28,000 tonnes by 1934. Landings of about 50,000 tonnes per year were sustained into the 1960’s but only because the fishermen began fishing in new waters.

The European fishing fleets consisted of groups of factory trawlers supplying mother ships that processed the catch and these had immense fishing and processing capacity (thousands of tons a day) much greater than local fleets.

In an hour a single factory trawler could catch 200 tons of fish, twice as much as a 16th century ship could have caught in a whole season’s fishing.

Fishing fleets were able to work cooperatively to exhaust aggregations of fish. When a concentration of fish was found (using the most sophisticated available search equipment) the trawlers would aggregate to fish it into oblivion before dispersing again to seek new schools.

Two Canadian fisheries scientists, Jeffrey Hutchings and Ransom Myers, have estimated that about eight million tons [7.25 million tonnes] of northern cod were caught between Cabot's arrival in 1497 and 1750, over the course of 25 to 40 cod generations.

Factory trawlers took the same amount in only 15 years, a period less than the lifetime of a single cod.

In the mid-1980’s U.S. fisheries scientists saw the collapse coming and pushed for major cuts in fish landings, but the fishing industry resisted cuts and it wasn’t until the mid 1990’s that reductions were imposed.

A similar process played out in Canadian waters. Canadian fisheries scientists overestimated sustainable yields of cod based on a series of bad assumptions. In the 1980’s 5x times as many cod were being taken as should have been removed.

Calls to cut back the fishery were ignored and by 1992 the fishery was finished.

However, habitat transformation almost certainly has played a major role.

Before trawling, the sea bottom on the banks was not a layer of mud. Rocks outcrops, boulders and stones provided structure, places for young fish to hide and rich communities of sponges, crabs, mussels, anemones, tube worms and other invertebrates flourished.

A bottom trawler’s net is held open by large metal doors weighing thousands of pounds and the bottom of the bag is kept on the seabed by a weighted metal cable. Each pass of a net drags boulders and rocks, buries and crushes invertebrates and leaves behind a virtual moonscape.

Bottom trawling is the ecological equivalent of clear-cutting, but carried out on a much more massive scale and out of view.